The objective of the proposed research is to gain an understanding of the mechanism(s) of C-C bond formation and cleavage reactions in the biosynthesis of certain terpenes and sterol precursors. The stereochemistry and substrate specificity of the enzymatic cyclizations of several diterpenes related to the plant growth hormone gibberellic acid are to be studied (collaboratively with Professor C. A. West) in cell-free and/or partially purified plant protein preparations. Total synthesis of and biosynthetic investigations with the unusual C-25 (sesterpene ?) lipid alcohols, moenocinol and diumycinol, are proposed. The stereochemistry of the multi-center biogentic-like olefin cyclization of linalyl-OPNB to terpinyl-OPNB is to be revealed through deuterium labelling studies. Similar cyclizations with neryl analogues bearing internal nucleophilic sites will elucidate the stereospecifity of these processes. Investigations upon the stereochemistry and substrate specificity of the presqualene to squalene biomimetic and biosynthetic transformation are also planned.